A typical digital system requires a large number of memory cells. Since the introduction of semiconductor memory, the number of storage states in an integrated circuit has been increasing at an exponential rate. In a conventional binary digital system, a memory cell can only store two states, "0" and "1", and a large number of memory cells are integrated to obtain large memory capacity. A resonant tunneling diode (RTD) has a folding current-voltage (I-V) characteristic. When the RTD is connected in series with a resistor or a current source as a load, there can be (N+1) stable operating points or storage states, where N is the number of current peaks of the RTD. When such multiple-valued storage states instead of binary states are used in a memory cell, the number of memory cells can be reduced.
U.S. Pat. No. 5,128,894 discloses that the number of stored states of N-peaked RTD memory cell can be increased to 2N+1 when a resistor is connected in series with the RTD to skew the I-V characteristic to a saw-tooth shape. The devices as taught were limited to a single node input-output line. In the continuation-in-part (CIP) application (Ser. No. 07/871806) and a negative power supply are used in a device as taught by the U.S. Pat. No. 5,128,894 that allows for the number of stored states to be doubled to 2(2N+1). Both of these teachings are restricted to using only a single node line input-output means for the memory cell.
Although a two-fold to four-fold increase in memory states represents is an improvement, it does not keep pace with the exponential increase in memory requirement of the present-day digital system. Furthermore, the power dissipation becomes a limiting factor when a very large number of 2(2N+1) type memory cells are connected in parallel. It is desirable to achieve a quantum increase in the number of storage states to accommodate the ever increasingly complex modern digital systems at minimum power dissipation. To accomplish this objective, a memory cell with a multiple node input-output from the device is disclosed below.